Re: [PATCH] coresight: cti: write regsiters directly in cti_enable_hw()

[Mike Leach]

Hi Tingwei

On Tue, 18 Aug 2020 at 12:11, Tingwei Zhang <tingwei@xxxxxxxxxxxxxx> wrote:
>
> Deadlock as below is triggered by one CPU holds drvdata->spinlock
> and calls cti_enable_hw(). Smp_call_function_single() is called
> in cti_enable_hw() and tries to let another CPU write CTI registers.
> That CPU is trying to get drvdata->spinlock in cti_cpu_pm_notify()
> and doesn't response to IPI from smp_call_function_single().
>
> [  988.335937] CPU: 6 PID: 10258 Comm: sh Tainted: G        W    L
> 5.8.0-rc6-mainline-16783-gc38daa79b26b-dirty #1
> [  988.346364] Hardware name: Thundercomm Dragonboard 845c (DT)
> [  988.352073] pstate: 20400005 (nzCv daif +PAN -UAO BTYPE=--)
> [  988.357689] pc : smp_call_function_single+0x158/0x1b8
> [  988.362782] lr : smp_call_function_single+0x124/0x1b8
> ...
> [  988.451638] Call trace:
> [  988.454119]  smp_call_function_single+0x158/0x1b8
> [  988.458866]  cti_enable+0xb4/0xf8 [coresight_cti]
> [  988.463618]  coresight_control_assoc_ectdev+0x6c/0x128 [coresight]
> [  988.469855]  coresight_enable+0x1f0/0x364 [coresight]
> [  988.474957]  enable_source_store+0x5c/0x9c [coresight]
> [  988.480140]  dev_attr_store+0x14/0x28
> [  988.483839]  sysfs_kf_write+0x38/0x4c
> [  988.487532]  kernfs_fop_write+0x1c0/0x2b0
> [  988.491585]  vfs_write+0xfc/0x300
> [  988.494931]  ksys_write+0x78/0xe0
> [  988.498283]  __arm64_sys_write+0x18/0x20
> [  988.502240]  el0_svc_common+0x98/0x160
> [  988.506024]  do_el0_svc+0x78/0x80
> [  988.509377]  el0_sync_handler+0xd4/0x270
> [  988.513337]  el0_sync+0x164/0x180
>
> This change write CTI registers directly in cti_enable_hw().
> Config->hw_powered has been checked to be true with spinlock holded.
> CTI is powered and can be programmed until spinlock is released.
>

Agreed.

Reviewed-by Mike Leach <mike.leach@xxxxxxxxxx>

> Fixes: 6a0953ce7de9 ("coresight: cti: Add CPU idle pm notifer to CTI devices")
> Signed-off-by: Tingwei Zhang <tingwei@xxxxxxxxxxxxxx>
> ---
>  drivers/hwtracing/coresight/coresight-cti.c | 17 +----------------
>  1 file changed, 1 insertion(+), 16 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-cti.c b/drivers/hwtracing/coresight/coresight-cti.c
> index 3ccc703dc940..869569eb8c7f 100644
> --- a/drivers/hwtracing/coresight/coresight-cti.c
> +++ b/drivers/hwtracing/coresight/coresight-cti.c
> @@ -86,13 +86,6 @@ void cti_write_all_hw_regs(struct cti_drvdata *drvdata)
>         CS_LOCK(drvdata->base);
>  }
>
> -static void cti_enable_hw_smp_call(void *info)
> -{
> -       struct cti_drvdata *drvdata = info;
> -
> -       cti_write_all_hw_regs(drvdata);
> -}
> -
>  /* write regs to hardware and enable */
>  static int cti_enable_hw(struct cti_drvdata *drvdata)
>  {
> @@ -112,15 +105,7 @@ static int cti_enable_hw(struct cti_drvdata *drvdata)
>         if (rc)
>                 goto cti_err_not_enabled;
>
> -       if (drvdata->ctidev.cpu >= 0) {
> -               rc = smp_call_function_single(drvdata->ctidev.cpu,
> -                                             cti_enable_hw_smp_call,
> -                                             drvdata, 1);
> -               if (rc)
> -                       goto cti_err_not_enabled;
> -       } else {
> -               cti_write_all_hw_regs(drvdata);
> -       }
> +       cti_write_all_hw_regs(drvdata);
>
>         config->hw_enabled = true;
>         atomic_inc(&drvdata->config.enable_req_count);
> --
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> a Linux Foundation Collaborative Project
>
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-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK